Midewin remains the only federal tallgrass prairie preserve east of the Mississippi River, where surviving areas of that habitat are extremely rare. With the adjacent Des Plaines Fish and Wildlife Area and a number of other state and county protected areas in the immediate area, Midewin forms the heart of a conservation macrosite totaling more than 40,000 acres of protected land.

The pre-European settlement vegetation map of Midewin shows most of the site was prairie prior to the arrival of European settlers.[3] The northwestern corner of the site along Jackson Creek was forest. Another small, forested area existed in the extreme southwest corner of Midewin along the Kankakee River and Prairie Creek.

Several not-for-profit conservation organizations have played active roles in the restoration of high-quality tallgrass prairie, dolomite prairie,[4] sedge meadows, swales and related communities at Midewin. These include the Wetlands Initiative, Openlands. and the Illinois chapter of The Nature Conservancy and several other members of the Chicago Wilderness collaborative.[5][6][7]

The Midewin National Tallgrass Prairie was established by federal law in 1996. Major proponents of the park's establishment and restoration included World War II flying aceWilliam J. Cullerton.[8]

The Illinois Land Conservation Act (Public Law 104-106) created the Midewin National Tallgrass Prairie, designated the transfer of 19,165 acres (7,756 ha) of land in Illinois from the U.S. Army to the U.S. Department of Agriculture's Forest Service.

The Illinois Land Conservation Act mandates that Midewin be managed to meet four primary objectives:

To conserve, restore, and enhance the native populations and habitats of fish, wildlife, and plants.

To provide opportunities for scientific, environmental, and land use education and research.

To allow the continuation of existing agricultural uses of lands within Midewin National Tallgrass Prairie for the next 20 years, or for compatible resource management uses thereafter.

To provide recreational opportunities that are compatible with the above purposes.

The first land transfer from the Army to the Forest Service took place on March 10, 1997, and included 15,080 acres (6,100 ha) of land that was believed to be free from contamination. Subsequent land acquisitions place the current size of Midewin at about 20,000 acres (8,100 ha).

After a period of ecological restoration, part of the prairie opened to visitors in 2004.

Today, over 7,000 acres (2,800 ha) acres of the reserve are open, with public trails for non-motorized recreation. The MNTP headquarters entrance is located on Illinois Route 53, near the center of the preserve.